The disclosure relates generally to additive manufacturing, and more particularly, to a method for correcting a three-dimensional model used for additive manufacturing based on defects identified using tomographic scanning.
Additive manufacturing (AM) includes a wide variety of processes of producing an object through the successive layering of material rather than the removal of material. As such, additive manufacturing can create complex geometries without the use of any sort of tools, molds or fixtures, and with little or no waste material. Instead of machining objects from solid billets of material, much of which is cut away and discarded, the only material used in additive manufacturing is what is required to shape the object.
Additive manufacturing techniques typically include taking a three-dimensional computer aided design (CAD) file of the object to be formed that includes an intended three-dimensional (3D) model or rendering of the object. The intended 3D model can be created in a CAD system, or the intended 3D model can be formulated from imaging (e.g., computed tomography (CT) scanning) of a prototype of an object to be used to make a copy of the object or used to make an ancillary object (e.g., mouth guard from teeth molding) by additive manufacturing. In any event, the intended 3D model is electronically sliced into layers, e.g., 18-102 micrometers thick, creating a file with a two-dimensional image of each layer. The file may then be loaded into a preparation software system that interprets the file such that the object can be built by different types of additive manufacturing systems. In 3D printing, rapid prototyping (RP), and direct digital manufacturing (DDM) forms of additive manufacturing, material layers are selectively dispensed to create the object.
In metal powder additive manufacturing techniques, such as selective laser melting (SLM) and direct metal laser melting (DMLM), metal powder layers are sequentially melted together to form the object. More specifically, fine metal powder layers are sequentially melted after being uniformly distributed using an applicator on a metal powder bed. The metal powder bed can be moved in a vertical axis. The process takes place in a processing chamber having a precisely controlled atmosphere of inert gas, e.g., argon or nitrogen. Once each layer is created, each two dimensional slice of the object geometry can be fused by selectively melting the metal powder. The melting may be performed by a high powered laser such as a 100 Watt ytterbium laser to fully weld (melt) the metal powder to form a solid metal. The laser moves in the X-Y direction using scanning mirrors, and has an intensity sufficient to fully weld (melt) the metal powder to form a solid metal. The metal powder bed is lowered for each subsequent two dimensional layer, and the process repeats until the three-dimensional object is completely formed.
In many additive manufacturing techniques, the layers are created following the instructions provided in the intended 3D model and use material either in a molten form or in a form that is caused to melt to create a melt pool. Each layer eventually cools to form a solid object. Imaging systems have been employed to ensure two-dimensional layers are formed accurately during additive manufacturing. However, one challenge with the cooling of the object is that a thermal defect can form in the object upon cooling, which prevents the object from conforming to the intended 3D model. The thermal defects typically cannot be identified during additive manufacturing because they are not present until later in the process. The thermal defects can also be difficult to identify after manufacturing because they are dimensionally very small and, oftentimes, are located in the object's interior. Current analysis techniques do not provide adequate mechanisms to identify the thermal defects and allow for corrections in the intended 3D model.